Security systems are commonly known in which a transmitter is connected to an entrance door which produces an audible indication or alarm when the door is opened. Furthermore, audible indication has been utilized to indicated conditions such as door bells.
U.S. Pat. No. 4,641,127, issued Feb. 3, 1987 in the name of Hogan et al discloses a security and fire protection system which utilizes a plurality of detection transmitter units which transmit unique signals corresponding to the specific type of condition. Such transmitter units may be detect the conditions of smoke, intrusion, or heat. A receiver alarm unit receives and decodes the signals produced by the detection transmitter units and produces an alarm signal indicating which type of detection transmitter has been actuated.
U.S. Pat. No. 4,777,474, issued Oct. 11, 1988 in the name of Clayton, discloses an alarm system for the hearing impaired which utilizes a base station provided with a radio transmitter for transmitting alarm signals, such as telephone, smoke/fire or door bell to a portable unit equipped with a receiver. The base station comprises a ring detect logic, smoke/fire alarm logic, front door logic, and burglar alarm logic hardwired to a telephone line, smoke/fire alarm, door bell push button, and burglar alarm, respectively. The logic circuits generate signals indicative of the alarm condition and are hardwired to an audio signal generator. The resulting audio signal generated by the audio signal generator is coupled to a low power FM transmitter for transmission to the portable receiver unit. An FM receiver receives the transmitted radio frequency signal via an antenna. The FM demodulator recovers the audio signal from the FM carrier and applies it to an ear phone via an audio preamplifier and audio driver. The patent teaches a wireless system comprising transmitter and receiver pairs wherein the receiver is capable of audibly indicating specific household conditions received from the transmitter via an rf signal created by an audio generator and logic circuitry that corresponds to the particular household condition.
U.S. Pat. No. 4,326,276, issued Apr. 20, 1982 in the name of Scott, Jr. discloses a musical door chime which is connected to the front and rear push buttons of a household. The chime is capable of playing a combination of musical tones when a door bell push button is actuated. The door bell push buttons are hardwired to a microprocessor. The musical tones which are played may be selected by a key board connected to a microprocessor. The musical door chime is capable of sounding a first musical tone when the front door bell push button is actuated and a second two-note musical tone when the rear door bell push button is actuated, and a third signal musical tone when the side door bell push button is actuated. However, the patent requires hardwiring between microprocessor and the push buttons which creates difficulty in installation.